The present invention relates generally to pavement marking, and more particularly to a seal arrangement for a lid of a kettle.
Alkyd and hydrocarbon thermoplastics are commonly used to mark pavement surfaces with visible lines and symbols such as lane dividers and guide lines. In particular, thermoplastics provide a durable alternative to pavement painting, and are commonly used to mark street intersections, parking lots, and other high-traffic pavement surfaces from which paint would quickly wear away.
Thermoplastics are conventionally applied to pavement surfaces using a mobile applicator comprising a heated reservoir or kettle, and an application screed die. Melted thermoplastic is dispensed from the kettle at a controlled rate and applied in a thin layer atop pavement surfaces with the screed die. Some applicators further comprise secondary burners which heat secondary reservoirs or screed die. Many applicators burn pressurized gas, such as propane and butane, at secondary burners and to heat applicator kettles. Manually driven and self-powered applicators are both relatively common, and some applicators can be attached to and driven by vehicles.
Conventional thermoplastics must be brought to melt temperatures of 177 to 250° C. (350 to 480° F.) prior to application. Existing systems use a central mixer-melter to bring thermoplastics to these temperatures. Once melted, a load of thermoplastic from the central mixer-melter is transferred to the kettle of a mobile applicator for pavement marking. The applicator kettle is heated to prevent thermoplastic from resolidifying before it is applied to the pavement surface. Often, a single central mixer-melter may service a plurality of applicators on a job site.
Due to the high temperatures at which thermoplastics melt, fumes can be released that are harmful to people. In addition, it takes a large amount of energy to heat the thermoplastics to those temperatures. And once the thermoplastics have cooled, they can adhere to the processing equipment and must be heated again for removal. While conventional kettles have lids to prevent some of these effects, they can be inefficient and easily fouled.